Carbohydrates It constitute one of the most important groups of natural

products.

Discovered in 1838 by a French

chemist “Anselm Payen”

Payen isolated it from plant

matter and he named as

cellulose, and also he determined

its chemical formula.

Suffix “ose”

In 1920 by the Hermann

Staudinger determined

the polymer structure of

cellulose.

Occurrence: widely distributed plant

polysaccharide.

main constituent of the

cell walls of plants, green

algae, bacteria and in

tunicates.

most abundant naturally

occurring biopolymer(Cotton,Wood)etc..,

Colourless solid

Non melting

Relatively hygroscopic

Thermal decomposition

starts at 180°

Ignition Point: ˃290°

Density:1.52-1.59 g/cm 2

Insoluble in water and in

organic solvents

Undergoes severe

degradation in

concentrated acids.

It readily soluble in cupra

ammonium hydroxide

solution(Schweizer’s

reagent)

Cellulose is linear homopolymer composed of

D-glucopyranose units linked by 1,4-β-D-glucosidic bonds.

The chemical formula is (C6H10O5 )n

The hydroxyl groups are positioned in the ring plane

(equatorial), while the hydrogen atoms are in the vertical

position (axial).

Sodium hydroxide solution at different concentrations

and different temperatures could dissolve cellulose with

different DP.

According to different solubilities under specific

conditions, cellulose can be divided into three types:

α-Cellulose

β-Cellulose

γ-Cellulose

1.Elementary analysis -(C6H10O5 )n

2.

Cellulose

Crystalline D- glucose

(indicates that it is

composed of D-glucose

only)

2.Acid

hydrolysis

Tri substituted cellulose

(indicates that only three hydroxyl groups

are free per glucose unit)

3.Acetylation,

Methylation,

Nitration.

4.Acetolysis

Cellobiose

Octa-acetate

(indicates that

it is composed

of cellobiose

units)

But it does not

indicate that

whether it is α

or β glycosidic

linkage.

Cellulose

(fully methylated)

5. Hydrolysis2,3,6-trimethyl glucose

2,3,4,6-tetramethyl glucose

Without any dimethyl glucose

•Indicates that free

hydroxyl groups are

present in C2,C3,C6

•Hence the two

glucose units are

linked through

C1 and C4 (pyranose)

(or)

C1 and C5 (furanose)

•Since glucose is not

easily hydrolyzed it

must be C1 and C4

Indicate that it has

chain length of

about 100-200

units .

Indicates that cellulose

is a linear polymer

Results :

The two D-glucose units are in the pyranose form

Linked via C1 and C4

Cellulose Cellobiose,Cellotriose,

Cellotetraose,Cellopentose,

Cellohexose,Celloheptaose.

6.Gentle acidic hydrolysis

•These products were isolated

by Zechmeister in 1931and

miller in 1960.

•All these had C1 and C4

links and also shown to be β

7.To determine whether cellulose is linear or branched.

Cellulose Solvents Colloidal solution Due to its largeness

Forms fibres

therefore it

must be linear

Finally the long length and linear structure is

confirmed by X-ray analysis

8.The structure of cellulose is assigned

9. Cellulose is not planar

The absence of free rotation about C-O-C link due

to steric effect give rise to a rigid chain molecule.

The long chains are held together by hydrogen

bonding and has a three dimensional brick work.

10. To determine the value of ‘n’

n is the chain length (or)the molecular size.

This is the only problem in establishing the structure

of cellulose.

This can be achieved by determining the molecular

weight.

The two methods are

• Chemical( Haworth methylation and Periodic

oxidation)

• Physical.

Haworth methylation: It is a in complete methylation in an inert atmosphere

followed by hydrolysis with dilute acid to cleave all

the glycosidic linkages.

Results:It is indicated that the presence of chain having 100 to

200 D-glucose residues which corresponds to molecular

weight of cellulose between 20,000 to 40,000.

Drawbacks:

This method always give low molecular weight of

cellulose because of incomplete methylation.

Periodic oxidation(Hirst method) It is based on the estimation of formic acid liberated by

the action of potassium metaiodate.

The reagent liberates 2 molecules of formic acid and one

of formaldehyde from the reducing end.

One molecule of formic acid from the non reducing end.

Results:Estimation of formic acid produced gives the value of

chain length as approximately 100 glucose units.

Drawbacks:

The results are uncertain since over oxidation also takes

place due to progressive attack on the chain molecule

from their reducing ends

Viscosity, osmotic pressure,ultra centrifugal

sedimentation.

These methods indicated that cellulose has

molecular weight of nearly 2000-3000

Results shows divergence therefore the value

of n is uncertain.

It may vary with the condition under which the

polysaccharide are synthesized.

X-Ray studies indicate that the length of unit

cell(10.25Å) corresponds to the length of two D-

glucopyranose units (6.15Å)

X-Ray diffraction pattern indicates that the cellulose

is not crystalline but it is partly crystalline and partly

amorphous

1.Mercerized (smoothed)cellulose:

eg-mercerized cotton used in clothing fabric

2.Regenerated cellulose:

To regenerate too short fibres to long fibres used

in the formation of rayon manufacture.

Prepared from viscose process.

Due to the presence of hydroxyl groups,it can be

converted into various useful derivatives.

1.Nitrocellulose or gun cotton

2.Cellulose acetates

Triacetate is used in photographic film and in textile

industry

Diacetate is used in production of plastics,safety film base.

Monoacetate is used in the manufacture of toys,knife

handle,motor car parts.

First discovered in 1859 by “Rouget” while he

was experimenting with chemical and thermal

manipulation of the natural fiber chitin.

1811 Chitin was first discovered by Professor Henri Braconnot,who isolated it from mushrooms and name it “Fungine”.

1823 Antoine Odier found chitin while studying beetle cuticles and named “chitin” after Greek word “chiton”. (tunic, envelope)

1859 Rouget discovered chitosan, a derivative of chitin.

1950s The structure of chitin and chitosan was identified by X-ray diffraction, infrared spectra, and enzymatic analysis.

Chitosan is the N-deacetylated derivative of chitin

It is a linear polysaccharide composed of

β(1 4) linked D-glucos-2-amine units.

It is white to light red solid powder, insoluble in water

but soluble inorganic acids.

Unique characteristics of chitin and chitosan:

• Biocompatible

• Biodegradable

• Non-toxic

• Remarkable affinity to proteins

• Ability to be functionalized

• Renewable

• Abundant

Moisture content-• It absorbs moisture from atmosphere.• Particle size distribution: <30 mm.• determined by the gravimetric method.Solubility-• Sparingly soluble in water.• Practically insoluble in ethanol and other organic

solvents.• Solubility is affected by degree of deacetylation.PH: 4.0-6.0Density: 1.35-1.40 g/cm3Glass transition temperature: 203°C

Chitosan is a linear polyamine.

It has reactive amino groups (-NH2).

There is availability of reactive hydroxyl groups(-OH).

It has chelating ability for many transition metal ions.

Wade.L.G, Organic chemistry, eighth edition,Pearson publications, 2017 Jain.J.L,Sunjay Jain,Nitin Jain, Fundamentals of Biochemistry ,S.Chand

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